The present invention relates to a tractor-drawn cultivator having a blade which cultivates the soil with air injected from a nozzle or injector provided on a lower portion of the blade which is forced into the soil.
Japanese Utility Model Laid-Open Nos. 57-125201 and 59-29102, for example, disclose cultivators each provided with an aerating device, attached to a tractor by a three-point linkage. The cultivator has a long vertical blade or shank provided with an injector at a lower portion thereof.
Such a cultivator is constructed to continuously inject compressed air from the injector at predetermined intervals. The cultivator is lowered by the three-point linkage to the surface of a field or fruit garden, and further the blade with the injector is inserted in the soil a predetermined sufficient depth to perform desired deep cultivation. The cultivation and aeration are performed while the tractor advances. When the operation is over, the cultivator is raised by the three-point linkage above the ground.
However, if the air is injected before the blade and injector reach the predetermined depth, the compressed air will spout out blowing up the soil. Consequently, holes are made in the field thereby affecting plants cultivated therein. It is also dangerous if the compressed air is discharged when the injector is above the ground.
In order to avoid such troubles, there have been proposed air injection systems. In one of the systems, a cultivator is provided with a valve in an air-supply passage to control the air flow. The drive of the cultivator opens the valve after the injector is sufficiently inserted in the soil. In another system, a vertically movable gauge wheel which automatically detects the position of the injector in the soil is provided to operate the valve when the injector reaches a predetermined position.
However, in the former system a mechanism for operating the valve is required. In addition, the driver must confirm that the injector is inserted the predetermined depth and perform a particular manual operation for opening the valve. In the latter, since a controlling means including the gauge wheel is provided, the machine becomes complicated in construction and heavy in weight. Moreover, each of both systems is constructed to inject air regardless of the air pressure in an air tank. Consequently, air may be injected into the soil at low pressure, resulting in insufficient cultivation.